Optical element and method for manufacturing the same

ABSTRACT

The present invention provides an optical element capable of improving the adhesion between the alignment property providing layer, for providing the alignment property to the refractive index anisotropic layer, and the refractive index anisotropic layer, as well as improving durability of each layer. 
     An optical element  10  comprises an alignment property providing layer  12  laminated on the transparent base material  11 , and a refractive index anisotropic layer  13  laminated on the alignment property providing layer  12 . The alignment property providing layer  12  is an alignment film which provides the alignment property to the refractive index anisotropic layer  13 . And the alignment property providing layer  12  is made from an alignment film composition capable of exhibiting the alignment limiting force by the photo-alignment method. The refractive index anisotropic layer  13  comprises a liquid crystal layer formed by curing (polymerizing) a liquid crystalline composition including a polymerizable liquid crystal material. In the refractive index anisotropic layer  13 , the curing degree of the refractive index anisotropic layer  13  changes monotonously with a predetermined gradient in its thickness direction such that, within the refractive index anisotropic layer  13 , the curing degree of the portion closer to the alignment property providing layer  12  is larger, compared with the curing degree of the portion farther from the alignment property providing layer  12 . It is preferable that the average curing degree of the refractive index anisotropic layer  13  is 90% or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element such as aretardation plate, a polarizing plate, and a color filter for a display.In particular, the invention relates to an optical element comprising aliquid crystal layer, made from a liquid crystalline compositionincluding a polymerizable liquid crystal material, as a refractive indexanisotropic layer, and a method for manufacturing the same. In thisspecification, the term “liquid crystal layer” is used for the meaningof a layer optically having the property of a liquid crystal, and thosehaving a solid phase state solidified while maintaining the moleculararrangement of the liquid crystal phase are also included as the layerstate.

2. Description of the Related Art

In general, the liquid crystal is used as a display medium such as adisplay element, represented by the TN (twisted nematic) type and theSTN (super twisted nematic) type, utilizing the reversible motility ofthe molecular arrangement. Also, the liquid crystal is used as anoptical element such as a retardation plate, a polarizing plate and acolor filter for a display, utilizing the alignment property and therefractive index anisotropy.

Here, as to the applications of the latter, recently, a large number ofoptical elements comprising a liquid crystal layer made from apolymerizable liquid crystal material, as a refractive index anisotropiclayer, have been proposed. Specifically, for example, Japanese PatentApplication National Publication (Laid-Open) No. 2002-533742 disclosesan optical element having the function of the wavelength selectivereflecting property and the polarization selective reflecting property,which is produced by using a special polymerizable liquid crystalcompound. Moreover, Japanese Patent Application Laid Open (JP-A) No.5-215921 discloses a birefringence plate produced by using apolymerizable liquid crystal compound having a rod like structure.Furthermore; JP-A Nos. 8-338913 and 9-152509 disclose an opticalcompensating sheet produced by using a polymerizable liquid crystalcompound having a disc like structure.

A generally used optical element has a supporting member, such as aplastic film, and a liquid crystal layer (refractive index anisotropiclayer) made from a polymerizable liquid crystal material laminated onthe supporting member via an alignment film.

Here, the alignment film provided in between the supporting member andthe refractive index anisotropic layer has the alignment limiting forceof limiting the alignment direction of the liquid crystal molecules inthe refractive index anisotropic layer. Such an alignment film can beformed by, for example, forming a polymer layer of a polyimide, apolyvinyl alcohol, gelatin, etc., having the alignment property, on thesupporting member, and subjecting the alignment treatment, such as arubbing treatment, to the polymer layer. In the case the rubbingtreatment is subjected as the alignment treatment, since the staticelectricity or the dusts are generated on the surface of the alignmentfilm, a technique, for making the alignment film to exhibit thealignment limiting force without subjecting the rubbing treatment, isstudied. The photo-alignment method is one of them, in which thealignment limiting force (anisotropy) is generated on the surface of thealignment film by irradiating light having an optional polarizationstate (polarized light). Such photo-alignment method includes: the“photo anisotropic type” of reversibly changing the alignment state bychanging only the molecule shape; and the “photo reaction type” ofchanging the molecules themselves. The latter “photo reaction type” canfurther be classified into the dimerization type, the decompositiontype, the coupling type, the decomposition-coupling type, or the like.

In the optical elements comprising the supporting member, the alignmentfilm and the refractive index anisotropic layer as explained above, itis of course important that the optical characteristics of each layer ofthe optical element are preferable. However, it is also important thatthe adhesion between the layers and the durability of each layer arepreferable. As to the latter problem, for example, if the adhesionbetween the alignment film and the refractive index anisotropic layerconstituting the optical element is poor, there is a problem that therefractive index anisotropic layer can be easily peeled off from thealignment film. Moreover, if the optical element is used or stored in ahigh temperature and high humidity environment, there is a problem thatmesh like wrinkles are generated in the refractive index anisotropiclayer.

In order to solve such problems, conventionally, the followingtechniques have been proposed.

That is, JP-A No. 9-152509 proposes a method in which a modifiedpolyvinyl alcohol is used, as the alignment film material, to improvethe adhesion between the layers due to chemical coupling at theinterface of the alignment film and the refractive index anisotropiclayer. Moreover, JP-A No. 10-10320 proposed a method in which theadhesion between these layers is improved by inserting an anchor coatinglayer in between layers of a low adhesion. Furthermore, Japanese PatentApplication National Publication (Laid-Open) No. 2000-514202 proposes amethod in which the durability of the refractive index anisotropic layeris improved by adding a monomer into the material of the refractiveindex anisotropic layer. Specifically, it proposes a method in which theglass transition temperature, the thermal stability and the mechanicalstability is changed by containing a non-mesogen compound having two orthree or more polymerizable functional groups by amount of 20% or lesswith respect to a reactive mesogen compound, as the refractive indexanisotropic layer material.

However, among the conventional methods mentioned above, in the methodmentioned in JP-A No. 9-152509, since the boiling point of the solvent,used for the modification reaction of the polyvinyl alcohol, is high,the coating solution including such solvent cannot be utilized.Therefore, a refining process of reprecipitation of the polyvinylalcohol is indispensable, and thus, there is a problem that themanufacturing cost is increased. Moreover, in the method disclosed inJP-A No. 10-10320, when the liquid crystal compound is used as thematerial for the refractive index anisotropic layer, there is a problemthat the liquid crystal molecules are not aligned preferably on theanchor coating layer. Furthermore, in the method mentioned in JapanesePatent Application National Publication (Laid-Open) No. 2000-514202, inthe case of providing the refractive index anisotropic layer by fixingthe alignment state of the liquid crystal molecules after the alignmenttreatment, the additives will be the impurities at the time of aligningthe liquid crystal molecules so that the alignment of the liquid crystalmolecules are inhibited. Thus, there is a problem that the opticalcharacteristics are deteriorated (for example, the display unevennessgeneration).

SUMMARY OF THE INVENTION

The present invention has been achieved in view of these points. Anobject thereof is to provide an optical element using a liquid crystallayer, made from a liquid crystalline composition including apolymerizable liquid crystal material, as the refractive indexanisotropic layer, capable of improving the adhesion between thealignment property providing layer, for providing the alignment propertyto the refractive index anisotropic layer, and the refractive indexanisotropic layer as well as improving durability of each layer, and amethod for manufacturing the same.

As the first means for solving the problems, the present inventionprovides an optical element comprising: a transparent base material; analignment property providing layer laminated on the transparent basematerial; and a refractive index anisotropic layer, laminated on thealignment property providing layer, with an alignment property providedby an alignment limiting force of the alignment property providinglayer, wherein the alignment property providing layer comprises analignment film made from an alignment film composition capable ofexhibiting the alignment limiting force by an photo-alignment method,and the refractive index anisotropic layer comprises a liquid crystallayer formed by curing a liquid crystalline composition including apolymerizable liquid crystal material, and a curing degree of therefractive index anisotropic layer changes monotonously with apredetermined gradient in its thickness direction such that, within therefractive index anisotropic layer, the curing degree of a portioncloser to the alignment property providing layer is larger, comparedwith the curing degree of a portion farther from the alignment propertyproviding layer.

In the above-described first means for solving the problems, it ispreferable that the average curing degree of the refractive indexanisotropic layer is 90% or higher.

Moreover, in the above-described first means for solving the problems,it is preferable that the liquid crystalline composition for forming therefractive index anisotropic layer includes a nematic liquid crystalcompound as the polymerizable liquid crystal material.

Furthermore, in the above-described first means for solving theproblems, it is preferable that the alignment film composition forforming the alignment property providing layer includes a polymer havinga cinnamoyl group. Here, it is preferable that the alignment filmcomposition includes a monomer or an oligomer having one or morefunctional groups, in addition to the polymer. Moreover, it ispreferable that the monomer or oligomer is a polymerizable liquidcrystal material. Furthermore, it is preferable that the polymerizableliquid crystal material in the alignment property providing layer andthe polymerizable liquid crystal material in the refractive indexanisotropic layer are a material of a same kind.

As second means for solving the problems, the present invention providesa method for manufacturing an optical element comprising: a step ofpreparing a transparent base material with an alignment film, made froma alignment film composition capable of exhibiting an alignment limitingforce by a photo-alignment method, laminated thereon as an alignmentproperty providing layer; a step of coating a liquid crystallinecomposition including a polymerizable liquid crystal material onto thealignment property providing layer of the transparent base material; anda step of forming a refractive index anisotropic layer, comprising aliquid crystal layer, whose curing degree changes monotonously with apredetermined gradient in its thickness direction, on the alignmentproperty providing layer of the transparent base material by curing theliquid crystalline composition while delaying a curing rate of theliquid crystalline composition near the surface on the side not adjacentto the alignment property providing layer, compared with the curing ratenear the surface on the side adjacent to the alignment propertyproviding layer.

In the above-described second means for solving the problems, it ispreferable that, in the step of forming the refractive index anisotropiclayer, a radioactive ray is irradiated to the liquid crystallinecomposition in a state that, among the liquid crystalline composition,only the side not adjacent to the alignment property providing layer isexposed to an air atmosphere. Here, it is preferable that theradioactive ray is an ultraviolet ray, and the liquid crystallinecomposition includes a polymerization initiator together with thepolymerizable liquid crystal material.

According to the first means for solving the problems of the presentinvention, the alignment property providing layer, for providing thealignment property to the refractive index anisotropic layer, comprisesan alignment film made from an alignment film composition capable ofexhibiting the alignment limiting force by an photo-alignment method,and also, the refractive index anisotropic layer comprises a liquidcrystal layer formed by curing a liquid crystalline compositionincluding a polymerizable liquid crystal material, and a curing degreeof the refractive index anisotropic layer changes monotonously with apredetermined gradient in its thickness direction such that, within therefractive index anisotropic layer, the curing degree of a portioncloser to the alignment property providing layer is larger, comparedwith the curing degree of a portion farther from the alignment propertyproviding layer. Therefore, adhesion between the alignment propertyproviding layer and the refractive index anisotropic layer is excellent.Furthermore, durability of each layer is excellent. Therefore, theproblem of peeling off of the refractive index anisotropic layer can besolved effectively. Moreover, when the average curing degree of therefractive index anisotropic layer is made to be 90% or higher, theadhesion with respect to the alignment property providing layer canfurther be improved. Moreover, even in the case the optical element isrolled up, a problem of blocking, caused by the refractive indexanisotropic layer sticking onto the rear surface of the transparent basematerial, can be prevented. Therefore, the problem of peeling off of therefractive index anisotropic layer, rising of the haze, unevennessgeneration or the like deriving from the alignment failure can be solvedmore effectively.

According to the second means for solving the problems of the presentinvention, a radioactive ray is irradiated to the liquid crystallinecomposition formed on the alignment property providing layer of thetransparent base material, with an alignment property provided, in astate that, among the liquid crystalline composition, only the side notadjacent to the alignment property providing layer is exposed to an airatmosphere. Thereby, the liquid crystalline composition is cured whiledelaying a curing rate of the liquid crystalline composition near asurface on the side not adjacent to the alignment property providinglayer, compared with the curing rate near a surface on the side adjacentto the alignment property providing layer. Thereby, the liquidcrystalline composition can be cured gradually and slowly from theportion on the alignment property providing layer side, toward theportion on the air interface side. Thus, the curing gradient isgenerated, such that the uncured component is increased as gettingcloser toward the portion on the air interface side, from the portion onthe alignment property providing layer side. Therefore, in the processof forming the refractive index anisotropic layer, the polymerizableliquid crystal material in the liquid crystalline composition is curedin a state that the shrinkage during curing is restrained as much aspossible. Thus, the adhesion of the liquid crystalline composition withrespect to the alignment property providing layer is maintained, as wellas the internal stress generated in the liquid crystalline compositionis alleviated. Thereby, the finally obtained optical element hasexcellent adhesion between the alignment property providing layer andthe refractive index anisotropic layer. Moreover, the durability of eachlayer will be excellent. Therefore, the problem of peeling off of therefractive index anisotropic layer, or generation of haze and unevennessderiving from the alignment failure can be solved more effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing an opticalelement according to an embodiment of the present invention;

FIG. 2 is a schematic graph showing the distribution of the curingdegree within a refractive index anisotropic layer of the opticalelement shown in FIG. 1;

FIG. 3 is a cross-sectional view schematically showing a modifiedexample of the optical element shown in FIGS. 1 and 2;

FIG. 4 is a cross-sectional view schematically showing another modifiedexample of the optical element shown in FIGS. 1 and 2;

FIG. 5 is a cross-sectional view schematically showing still anothermodified example of the optical element shown in FIGS. 1 and 2;

FIG. 6 is a cross-sectional view schematically showing still anothermodified example of the optical element shown in FIGS. 1 and 2; and

FIG. 7 is a process diagram for explaining a method for manufacturing anoptical element according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention will be explained,referring to the drawings.

First, referring to FIGS. 1 and 2, the configuration of an opticalelement in an embodiment of the present invention will be explained.

As shown in FIG. 1, an optical element 10 in this embodiment comprises atransparent base material 11, an alignment property providing layer 12laminated on the transparent base material 11, and a refractive indexanisotropic layer 13 laminated on the alignment property providing layer12.

Among them, the transparent base material 11 is a supporting member,made from a glass, a transparent resin film or the like, for supportingthe alignment property providing layer 12 and the refractive indexanisotropic layer 13. Here, as the transparent resin film, a film madefrom: the cellulose based resins such as a triacetate cellulose (TAC), adiacetyl cellulose, and an acetate butylate cellulose; the polyesterbased resins such as a polyethylene terephthalate (PET) and a polyester;the olefin based resins such as a polyethylene; as a polyacrylic basedresins; a polyurethane based resins; resins such as a polyether sulfon,a polycarbonate, a polysulfone, a polyether, a polymethyl pentene, apolyether ketone, and a (meth)acrylonitrile can be used. As such atransparent resin film, a film made from a triacetate cellulose (TAC)having no birefringence can be used preferably.

It is preferable that the transparent base material 11 has the thicknessof about 25 μm to 1,000 μm. Moreover, the transparent base material 11may be a continuous long film having a certain length. Morespecifically, it may be a continuous film supplied in a rolled up state,which is commonly used industrially. The length of such a long film maybe set optionally. In the case of a rolled up embodiment, for example,it may be as long as about 10,000 m.

The alignment property providing layer 12 is an alignment film havingthe alignment limiting force which provides the alignment property tothe refractive index anisotropic layer 13. And the alignment propertyproviding layer 12 is made from an alignment film composition capable ofexhibiting the alignment limiting force by the photo-alignment method.It is preferable that the thickness of the alignment property providinglayer 12 is about 0.01 μm to 0.5 μm. Here, the photo-alignment method isa method to make the surface of the alignment film to exhibit thealignment limiting force (anisotropy) by irradiating light, having anoptional polarization state (polarized light), to the alignment film.

Here, as a alignment film composition for forming the alignment propertyproviding layer 12, a polymer, a coupling agent or the like can be used.Specifically, the examples of the polymer include polymers such as apolymethyl methacrylate, an acrylic acid-methacrylic acid copolymer, astyrene-maleinimide copolymer, a polyvinyl alcohol, a modified polyvinylalcohol, a gelatin, a styrene-vinyl toluene copolymer, achlorosulfonated polyethylene, a nitrocellulose, a polyvinyl chloride, apolyolefin chloride, a polyester, a polyimide, a vinyl acetate-vinylchloride copolymer, an ethylene-vinyl acetate copolymer, a carboxymethyl cellulose, a polyethylene, a polypropylene and a polycarbonate.Moreover, as the examples of the coupling agent, a silane coupling agentor the like can be presented.

As mentioned above, the photo-alignment method, which makes thealignment property providing layer 12 made from such a alignment filmcomposition to exhibit the alignment limiting force, includes: the“photo anisotropic type” of reversibly changing the alignment state bychanging only the molecule shape; and the “photo reaction type” ofchanging the molecules themselves The latter “photo reaction type” canfurther be classified into the dimerization type, the decompositiontype, the coupling type, the decomposition-coupling type or the like.Among them, as an example of the “dimerization” technique commonly usedas the photo-alignment method, in the technique, chemical reaction suchas the dimerization reaction is brought about in the polarizationdirection thereof on the surface of the alignment film by irradiatinglight having an optional polarization state (polarized light), so as toexhibit the alignment limiting force. As a representative of the polymercapable of exhibiting the alignment limiting force by such“dimerization”, a polyvinyl cinnamate (PVCi) can be presented. In suchpolyvinyl cinnamate (PVCi), by the dimerization reaction, a double bondportion of two side chains, parallel to the polarized light, is openedand re-coupled with each other by irradiating for example a polarizedultraviolet ray. As other polymers capable of exhibiting the alignmentlimiting force by such “dimerization”, a polymer having a cinnamoylgroup, a coumarin group, a carchon group or the like can be usedpreferably (see for example JP-A Nos. 7-138380 and 10-324690).

To the above-described alignment film composition, in addition to theabove-described polymers, a monomer or an oligomer having one or morefunctional groups may be added. As such monomer or oligomer, amonofunctional monomer having a functional group such as an acrylatebased ones and a cinnamoyl based ones (such as a reactive ethyl(meth)acrylate, an ethyl hexyl (meth)acrylate, a styrene, a methylstyrene, and a N-vinyl pyrrolidone), a polyfunctional monomer (such as apolymethylol propane tri (meth)acrylate, a hexane diol (meth)acrylate, atriethylene (polypropylene) glycol diacrylate, a tripropylene glycoldi(meth)acrylate, a diethylene glycol di(meth)acrylate, apentaerythritol tri(meth)acrylate, a dipentaerythritolhexa(meth)acrylate, a 1,6-hexane diol di(meth)acrylate, a neopentylglycol di(meth)acrylate, and an isocyanuric acid EO modifieddiacrylate), a bisphenol fluorene derivative (such as a bisphenoxyethanol fluorene diacrylate, and a bisphenol fluorene diepoxy acrylate)or the like can be used alone or as a mixture. Since the structure ofthe alignment property providing layer 12, made from the alignment filmcomposition, will be a firm mesh structure by adding such a monomer oroligomer to the alignment film composition, the strength of thealignment property providing layer 12 itself can be improved. Moreover,since the monomer or oligomer in the alignment property providing layer12 is cross linked, in the vicinity of the interface of the alignmentproperty providing layer 12 and the refractive index anisotropic layer13, with the molecules in the refractive index anisotropic layer 13adjacent to the alignment property providing layer 12, the adhesionbetween the alignment property providing layer 12 and the refractiveindex anisotropic layer 13 can be improved as well.

Here, the adding amount of the above-described monomer or oligomer canbe adjusted optionally in a range not to deteriorate the opticalcharacteristics of the optical element 10, as long as the adhesionbetween the alignment property providing layer 12 and the refractiveindex anisotropic layer 13 can sufficiently be improved. However, ingeneral, it is preferably 0.01% by weight or more and 3% by weight orless with respect to the solid component (polymer) weight. When it isless than 0.01% by weight, the effect of improving the adhesion betweenthe alignment property providing layer 12 and the refractive indexanisotropic layer 13 cannot be exhibited sufficiently. On the otherhand, when it is more than 3% by weight, even though the effect ofimproving the adhesion between the alignment property providing layer 12and the refractive index anisotropic layer 13 is sufficient, thealignment property may not be provided sufficiently to the refractiveindex anisotropic layer 13. That is, as it will be described later, therefractive index anisotropic layer 13 is obtained by going through theprocesses of aligning the liquid crystal molecules and fixing of thealignment state thereof. Since the above-described monomer or oligomeris an alignment inhibiting substance at the time of aligning the liquidcrystal molecules, rising of the haze, unevenness generation or the likedue to the alignment failure may be brought about. Thus, the opticalfunction may be deteriorated.

Moreover, it is preferable that the above-described monomer or oligomeris a polymerizable liquid crystal material. In particular, it ispreferable that such monomer or oligomer made from the polymerizableliquid crystal material is a material of the same kind as thepolymerizable liquid crystal material in the refractive indexanisotropic layer 13. Thereby, the monomer or oligomer in the alignmentproperty providing layer 12 can be cross linked with the molecules inthe refractive index anisotropic layer 13 adjacent to the alignmentproperty providing layer 12 more easily. Thus, the adhesion between thealignment property providing layer 12 and the refractive indexanisotropic layer 13 can further be improved.

Furthermore, in the case the transparent base material 11 is a longfilm, and is rolled up at the time the alignment property providinglayer 12 is laminated on the transparent base material 11, it ispreferable that the kind and the adding amount of the monomer oroligomer are adjusted optionally such that the alignment propertyproviding layer 12 can be close to a solid at an ordinary temperature.In this case, as the kind of the monomer or oligomer, it is preferableto use those of high molecular weight. Thereby, even in the case thetransparent base material 11 is rolled up at the time the alignmentproperty providing layer 12 is laminated thereon, the problem ofblocking, generated by sticking of the alignment property providinglayer 12 onto the rear surface of the transparent base material 11, dosenot occur.

The refractive index anisotropic layer 13 is an optical functional layerfor exhibiting the function as a retardation plate, a polarizing plate,a color filter for a display or the like. The refractive indexanisotropic layer 13 comprises a liquid crystal layer formed by curing(polymerizing) a liquid crystalline composition including apolymerizable liquid crystal material. In the refractive indexanisotropic layer 13, as shown in FIG. 2, the curing degree of therefractive index anisotropic layer 13 changes monotonously with apredetermined gradient in its thickness direction such that, within therefractive index anisotropic layer 13, the curing degree of the portioncloser to the alignment property providing layer 12 is larger, comparedwith the curing degree of the portion farther from the alignmentproperty providing layer 12. Here, the “surface” of FIG. 2 denotes aninterface between the refractive index anisotropic layer 13 and the air.The “rear surface” of FIG. 2 denotes an interface between the refractiveindex anisotropic layer 13 and the alignment property providing layer12. Moreover, it is preferable that the average curing degree of therefractive index anisotropic layer 13 is 90% or more. Here, the“monotonous change” denotes increase or decrease of the curing degree inits thickness direction with a certain tendency, and it is not limitedto the linear change, but it also includes an optional change such as aquadratic curve and an exponential curve. Moreover, it is not limited tothe monotonous change in a strict sense (monotonous increase ormonotonous reduction), but it also includes a stepwise increase ordecrease. Moreover, the “average curing degree” is the average value ofthe curing degree in its thickness direction as a whole of therefractive index anisotropic layer 13.

The thickness of the refractive index anisotropic layer 13 is determinedby the desired optical characteristics.

Here, in addition to the below-described polymerizable liquid crystalmaterials, it is preferable that the liquid crystalline composition forforming the refractive index anisotropic layer 13 includes optionaladditives (such as a polymerization initiator, a plasticizing agent, asurfactant and a silane coupling agent) in a range not to influence thealignment of the liquid crystal material or the optical characteristics.The adding amount of the additive can be adjusted optionally accordingto the liquid crystal material and the like in the liquid crystallinecomposition. However, in general, it is preferably 0.001% by weight ormore and 10% by weight or less with respect to the solid component(polymerizable liquid crystal material) weight. Moreover, although sucha liquid crystalline composition can be coated as it is, on thealignment property providing layer 12, it may also be dissolved in anappropriate solvent such as an organic solvent, in order to match theviscosity to a coating device or to obtain a preferable alignment state.

On the other hand, as a polymerizable liquid crystal material includedin such a liquid crystalline composition, a nematic liquid crystalcompound having a nematic regularity can be used preferably.Specifically, the compounds disclosed in JP-A No. 7-258638, JapanesePatent Application National Publication (Laid-Open) No. 10-508882, andJP-A No. 2003-287623 can be used optionally. More specifically, it ispreferable to use the compounds represented by the following chemicalformulae (1) to (10).

However, the nematic liquid crystal compound to be used in thisembodiment is not limited to the above-mentioned ones, but optional onescan be used as long as it is a liquid crystal compound with a nematicliquid crystal property, having one or more functional groups (such as aultraviolet ray curing polymerizable group) on the end. Moreover, amongthe above-described nematic liquid crystal compounds, a several kinds ofthe materials can be mixed and used optionally.

Here, the liquid crystalline composition including such a nematic liquidcrystal composition is coated on the alignment property providing layer12 by the below-described methods and is cured (polymerized) byirradiating a ultraviolet ray or the like. The accordingly formedfinally obtained refractive index anisotropic layer 13 may comprise, asshown in FIG. 1, a liquid crystal layer with the nematic liquid crystalmolecules fixed in a state that molecules are aligned in parallel withrespect to the transparent base material 11. Otherwise, as therefractive index anisotropic layer 13A shown in FIG. 3, the layer maycomprise a liquid crystal layer with the nematic liquid crystalmolecules fixed in a state that molecules are aligned vertically withrespect to the transparent base material 11. The liquid crystalstructure of the refractive index anisotropic layer 13 shown in FIG. 1is a homogeneous structure (parallel alignment structure). With thisstructure, an optical functional layer referred to as an A plate can beobtained. On the other hand, the liquid crystal structure of therefractive index anisotropic layer 13A shown in FIG. 3 is a homeotropicstructure (vertical alignment structure). With this structure, anoptical functional layer referred to as a positive (+) C plate can beobtained.

On the other hand, as the polymerizable liquid crystal material includedin the liquid crystalline composition, a mixture of the polymerizablenematic liquid crystal compound and a chiral agent may be used (see JP-ANo. 2003-287623). The chiral agent is used for the purpose of inducingthe helical structure in the nematic regularity exhibited by the nematicliquid crystal compound. As long as this purpose is achieved, optionalkinds satisfying the following can be used: compatible with the nematicliquid crystal compound in a solution state or a molten state; andcapable of inducing a desired helical structure without deterioratingthe liquid crystal property of the nematic liquid crystal compound.Specifically, for example, it is preferable to use a low molecularcompound having the axial asymmetry within the molecule, represented bythe following general formulae (11), (12), or (13).

In the above-mentioned general formulae (11) or (12), R4 denotes ahydrogen or a methyl group. Y is an optional one of the above-mentionedformulae (i) to (xxiv). Among them, it is preferably any one of theformulae (i), (ii), (iii), (v) and (vii). Moreover, c and d,representing the chain length of an alkylene group can eachindependently be an optional integer in a range of 2 to 12. They arepreferably in a range of 4 to 10, and further preferably in a range of 6to 9. When the value c or d is 0 or 1, the compounds of theabove-mentioned general formula (II) or (12) lack in stability, easilyhydrolyzed, and have a high crystal property. On the other hand, whenthe value c or d is 13 or more, the compounds have low melting point(Tm). In these compounds, the compatibility with respect to thepolymerizable liquid crystal material showing the nematic regularity maybe lowered. Therefore, depending on the concentration, the phaseseparation or the like may occur. There is no need that such chiralagent has the polymerization property, in particular. However, in thecase the chiral agent has the polymerization property, since it ispolymerized with the polymerizable liquid crystal material showing thenematic regularity so that the cholesteric regularity can be fixedstably, it is extremely preferable in terms of the thermal stability orthe like. In particular, it is preferable that the both ends of themolecule have a polymerizable functional group, in terms of obtainingthe refractive index anisotropic layer 13 having a preferable heatresistance.

In this case, as the refractive index anisotropic layer 13B shown inFIG. 4, the finally obtained refractive index anisotropic layer, whichis formed on the alignment property providing layer 12, comprises aliquid crystal layer with the nematic liquid crystal molecules fixed ina state of a helical structure of the planar alignment (state having thecholesteric regularity) with respect to the transparent base material11. In this case, the liquid crystal structure of the refractive indexanisotropic layer 13B is the cholesteric structure. With this structure,an optical functional layer referred to as a negative (−) C plate can beobtained.

As the refractive index anisotropic layer 13C shown in FIG. 5, in thefinally obtained refractive index anisotropic layer formed on thealignment property providing layer 12, the refractive index anisotropiclayer 13 shown in FIG. 1 and the refractive index anisotropic layer 13Bshown in FIG. 4 may be laminated on each other. Besides the above, amongthe liquid crystal layers 13, 13A, 13B shown in FIGS. 1, 3 and 4, two ormore layers, of the same kind or different kinds, may be laminated oneach other.

Moreover, as shown in FIG. 6, a barrier layer (intermediate layer) 14for blocking the elution of a plasticizing agent or the like included inthe transparent base material 11 may be provided in between thetransparent base material 11 and the alignment property providing layer12. As the material for the barrier layer 14, for example, anultraviolet ray curing type acrylic urethane based resin, an ultravioletray curing type polyester acrylate based resin, an ultraviolet raycuring type epoxy acrylate based resin, an ultraviolet ray curing typepolyol acrylate based resin, an ultraviolet ray curing type epoxy resinor the like can be presented. Generally, the ultraviolet ray curing typeacrylic urethane based resin can be obtained easily by reacting apolyester polyol with an isocyanate monomer or prepolymer, and furtherreacting the obtained product with an acrylate based monomer having ahydroxyl group such as a 2-hydroxy ethyl acrylate, a 2-hydroxy ethylmethacrylate (hereinafter, with the premise that the acrylate includesthe methacrylate, only the acrylate will be shown), and a2-hydroxypropyl acrylate. Generally, the ultraviolet ray curing typepolyester acrylate based resin can be obtained easily by reacting apolyester polyol with a 2-hydroxy ethyl acrylate or a 2-hydroxy acrylatebased monomer. As the specific examples of the ultraviolet ray curingtype epoxy acrylate based resin, one prepared by making an epoxyacrylate into an oligomer, and adding a reactive diluting agent and aphoto reaction initiator thereto for reaction can be presented. As thephoto reaction initiator, one kind or two or more kinds of a benzoinderivative, an oxime ketone derivative, a benzophenone derivative, athioxantone derivative or the like can be selected and used. Moreover,as the specific examples of the ultraviolet ray curing type polyolacrylate based resin, a trimethylol propane triacrylate, a ditrimethylolpropane tetraacrylate, a pentaerythritol triacrylate, a pentaerythritoltetraacrylate, a dipentaerythritol hexaacrylate, an alkyl modifieddipentaerythritol pentaacrylate or the like can be presented. Theseresins are generally used together with a known photo sensitizer.

Here, in consideration to the improvement of the adhesion between thebarrier layer 14 and the alignment property providing layer 12, asmentioned above, it is preferable to add a monomer or an oligomer havingone or more functional groups to the alignment film composition forforming the alignment property providing layer 12. Also, as the materialfor the barrier layer 14, it is preferable to add the monomer or theoligomer of the same kind as the monomer or the oligomer to be added tothe alignment film composition. Thereby, as in the above-mentioned case(in the case of improving the adhesion between the alignment propertyproviding layer 12 and the refractive index anisotropic layer 13), theadhesion between the barrier layer 14 and the alignment propertyproviding layer 12 can be improved due to the cross linking of themonomer or the oligomer in the barrier layer 14 with the molecules inthe alignment property providing layer 12 adjacent to the barrier layer14.

Instead of the barrier layer 14, an intermediate layer such as anadhesive layer, for improving the adhesion between the transparent basematerial 11 and the alignment property providing layer 12, may beprovided.

Next, referring to FIG. 7, the method for manufacturing the opticalelement 10 having such a configuration will be explained.

First, as the transparent base material 11, for example, a transparentresin film is prepared (FIG. 7A). Then, the barrier layer 14 is formedon one side surface of the transparent base material 11 (FIG. 7B).

In the case, for example, an ultraviolet ray curing resin is used as thematerial for the barrier layer 14 to be formed on the transparent basematerial 11, after coating the barrier layer composition, it is cured(polymerized) by irradiating an ultraviolet ray or the like.

Next, by coating a alignment film composition, including a polymer and acoupling agent, on the barrier layer 14 formed on the transparent basematerial 11, a coated film 12′ of the alignment film composition isformed (FIG. 7C). At the time, the alignment film composition is coatedin a form of a solution of the alignment film composition obtained bydissolving in an organic solvent. As the coating method, for example,spin coating, bar coating, extrusion coating, direct gravure coating,reverse gravure coating, die coating or the like can be used, but it isnot limited thereto.

Thereafter, a heated-air drying process is applied to the coated film12′ of the alignment film composition, accordingly formed on the barrierlayer 14, by applying the heat H, and then, an ultraviolet ray L1 havingan optional polarization state is irradiated thereto. Thereby, thealignment limiting force is exhibited on the surface of the coated film12′ of the alignment film composition so that an alignment propertyproviding layer 12 as the alignment film is formed (FIG. 7D).

Next, a coated film 13′ of the liquid crystalline composition is formedby coating a liquid crystalline composition, including a polymerizableliquid crystal material, on the alignment property providing layer 12accordingly formed on the barrier layer 14 (FIG. 7E). At the time, theliquid crystalline composition is coated in a form of a solution of theliquid crystalline composition obtained by dissolving in an organicsolvent. As the coating method, for example, spin coating, bar coating,extrusion coating, direct gravure coating, reverse gravure coating, diecoating or the like can be used, but it is not limited thereto.

Thereafter, by applying a heated-air drying process to the coated film13′ of the liquid crystalline composition accordingly formed on thealignment property providing layer 12, the alignment direction of theliquid crystal molecules in the coated film 13′ of the liquidcrystalline composition is limited by the alignment limiting forceexhibited on the surface of the alignment property providing layer 12.Thus, a coated film 13″ of the liquid crystalline composition, with thealignment property provided, is formed (FIG. 7F).

Then, by irradiating an ultraviolet ray (radioactive ray) L2, as theenergy line, to the coated film 13″ of the liquid crystallinecomposition accordingly provided with the alignment property for curing(polymerizing) the coated film 13″ of the liquid crystallinecomposition, the alignment state of the liquid crystal molecules isfixed. At the time, the ultraviolet ray L2 is irradiated to the coatedfilm 13″ of the liquid crystalline composition in a state that, amongthe coated film 13″ of the liquid crystalline composition, only the sidenot adjacent to the alignment property providing layer 12 is exposed toan air atmosphere. Thereby, the coated film 13″ of the liquidcrystalline composition is cured while delaying a curing rate of thecoated film 13″ of the liquid crystalline composition near a surface onthe side not adjacent to the alignment property providing layer 12,compared with the curing rate near a surface on the side adjacent to thealignment property providing layer 12. That is, when a surface of thecoated film 13″ of the liquid crystalline composition is irradiated withthe ultraviolet ray L2 for curing in a state being exposed to an airatmosphere, the curing of the radical polymerization type compound orthe like including a (meth) acryloyl group is inhibited by the oxygen,on the air interface side surface of the coated film 13″ of the liquidcrystalline composition. Thus, the vicinity of the air interface sidesurface of the coated film 13″ of the liquid crystalline composition ismade more difficult to be cured. Therefore, within the coated film 13″of the liquid crystalline composition, the curing progresses graduallyand slowly from the portion on the alignment property providing layer 12side to the portion on the air interface side so that the curinggradient will be generated such that the uncured component increasesfrom the portion on the alignment property providing layer 12 side tothe portion on the air interface side. Thereby, the refractive indexanisotropic layer 13 comprising a liquid crystal layer, whose curingdegree changes monotonously with a predetermined gradient in itsthickness direction, is formed on the alignment property providing layer12 (FIG. 7G). The curing degree of the refractive index anisotropiclayer 13 accordingly formed is preferably about 99% near the alignmentproperty providing layer 12 side, and about 85% near the air interfaceside. The average curing degree of the finally obtained refractive indexanisotropic layer 13 is preferably 90% or more. In the process ofgenerating the curing gradient as mentioned above, after forming therefractive index anisotropic layer 13, an ultraviolet ray may beirradiated again for sufficient curing.

The curing state of the refractive index anisotropic layer 13 can befound out by observing the residual amount of the reactive groups.Moreover, in order to observe the curing degree distribution within thelayer of the refractive index anisotropic layer 13, a cross-sectionalsurface of the layer should be produced. Therefore, in a specificmeasuring method, first, the refractive index anisotropic layer 13 iscut by the oblique cutting method. If the refractive index anisotropiclayer 13 is cut obliquely, since the cross-sectional surface obtainedthereby has the apparent thickness larger than the ordinarycross-sectional surface, the spatial resolution can be made higher atthe time of observing the residual amount of the reactive groupsthereafter. Next, after accordingly obtaining the cross-sectionalsurface of the refractive index anisotropic layer 13, the residualamount of the reactive groups is observed. As representative methods forobserving the residual amount of the reactive groups, the followingmethods can be presented: a method in which the molecular vibrationderiving from the reactive groups is observed by the infrared rayabsorption; and a method in which the mass attributing to the reactivegroup structure is measured. More specifically, (1) a method in whichthe intensity distribution of the stretching vibration of the doublebond (C═C) of the carbons attributing to the reactive groups is measuredby using the reflection measuring method of a microscope infraredspectrophotometer, (2) a method in which the mass number deriving fromthe reactive groups is mapped by using a Time of Flight Secondary IonMass Spectrometry (TOF-SIMS), (3) a method in which the signal intensityderiving from the reactive groups of all the carbons is measured byusing an X ray photoelectron spectroscopy device, or the like can bepresented. It is not limited to these measuring methods using astructure analysis technique, but the curing state of the refractiveindex anisotropic layer 13 can be found out also by methods of measuringthe surface hardness of the cross-sectional surface of the refractiveindex anisotropic layer 13 using a minute curing meter or a nanoindenter.

The curing degree is described by % in the present invention. Theconnection between the measured values (signal intensity) obtained fromthe above measurement methods: (1), (2) and (3), and the curing degree %is acquired by the following criterion. That is, since the refractiveindex anisotropic layer is formed by irradiating an ultraviolet ray tothe coated film of the liquid crystalline composition which is formed byapplying the liquid crystalline composition comprising the polymerizableliquid crystal material, each measured values (signal intensity)regarding the coated film, before the ultraviolet ray irradiation,obtained by the above (1), (2) and (3) is referred to as 0% in curingdegree, while the signal intensity 0 obtained in the above (1), (2) and(3) is regarded as 100% in curing degree.

Moreover, the atmosphere, to which the side not adjacent to thealignment property providing layer 12 of the coated film 13″ of theliquid crystalline composition is exposed, is not limited to the airatmosphere. Depending on the kind of the polymerizable liquid crystalcompound included in the liquid crystalline composition, it can beexposed to an atmosphere including water. That is, in a cationpolymerization compound or the like including an epoxy group, curinginhibition is brought about by water. Therefore, in the case of a liquidcrystalline composition including such a liquid crystal compound, as inthe above-mentioned case of the air atmosphere, the curing gradient,such that the uncured component is increased from the portion on thealignment property providing layer 12 side toward the portion on theatmosphere interface, can be generated.

Furthermore, it is preferable that the ultraviolet ray L2 to beirradiated to the coated film 13″ of the liquid crystalline compositionis irradiated only for a short time, with a high illuminance. Forexample, it is preferable to irradiate the coated film 13″ with a 100 mWilluminance for only 2 seconds. Moreover, it is preferable that theultraviolet ray L2 is a light including a wavelength in a range of 100nm to 450 nm, and more preferably a light including a wavelength in arange of 250 to 400 nm. The light of a wavelength in this range caneasily be obtained by a common light source, and by utilizing a generalcommercially available polymerization initiator, the chemical reactionsuch as the ultraviolet ray curing can be obtained more easily andefficiently.

The ultraviolet ray L2 is used as the radioactive ray to be irradiatedto the coated film 13″ of the liquid crystalline composition for formingthe refractive index anisotropic layer 13. However, as such aradioactive ray, optional ones can be used as long as it can cure theabove-described polymerizable liquid crystal material. Other than theultraviolet ray, an electron beam, a visible light, an infrared ray(heat ray) or the like can be used optionally according to theconditions. However, from the viewpoint of the process easiness or thelike, the ultraviolet ray is preferable.

In this embodiment, the alignment property providing layer 11, forproviding the alignment property to the refractive index anisotropiclayer 13, comprises an alignment film made from a alignment filmcomposition capable of exhibiting the alignment limiting force by thephoto-alignment method. Also, the refractive index anisotropic layer 13comprises a liquid crystal layer formed by curing a liquid crystallinecomposition including a polymerizable liquid crystal material, and thecuring degree of the refractive index anisotropic layer 13 changesmonotonously with a predetermined gradient in its thickness directionsuch that, within the refractive index anisotropic layer 13, the curingdegree of the portion closer to the alignment property providing layer12 is larger, compared with the curing degree of the portion fartherfrom the alignment property providing layer 12. Therefore, the adhesionbetween the alignment property providing layer 12 and the refractiveindex anisotropic layer 13 is excellent, and the durability of eachlayer is excellent. Thus, the problem of peeling off of the refractiveindex anisotropic layer 13 can be solved effectively.

In particular, in this embodiment, for the coated film 13″ of the liquidcrystalline composition, provided with the alignment property, formed onthe alignment property providing layer 12 of the transparent basematerial 11, the ultraviolet ray L2 is irradiated to the coated film 13″of the liquid crystalline composition in a state that, among the coatedfilm 13″ of the liquid crystalline composition, only the side notadjacent to the alignment property providing layer 12 is exposed to anair atmosphere. And the coated film 13″ of the liquid crystallinecomposition is cured while delaying the curing rate of the coated film13″ of the liquid crystalline composition near the surface on the sidenot adjacent to the alignment property providing layer 12, compared withthe curing rate near the surface on the side adjacent to the alignmentproperty providing layer 12. Thereby, within the coated film 13″ of theliquid crystalline composition, the curing progresses gradually andslowly from the portion on the alignment property providing layer 12side toward the portion on the air interface side, so as to generate thecuring gradient such that the uncured component increases from theportion on the alignment property providing layer 12 side toward theportion of the air interface. Therefore, in the process of forming therefractive index anisotropic layer 13, the polymerizable liquid crystalmaterial in the coated film 13″ of the liquid crystalline composition iscured in a state that the curing shrinkage is restrained as much aspossible. Thus, the adhesion of the coated film 13″ of the liquidcrystalline composition with respect to the alignment property providinglayer 12 is maintained, as well as the internal stress generated withinthe coated film 13″ of the liquid crystalline composition is alleviated.Thereby, in the finally manufactured optical element 10 the adhesionbetween the alignment property providing layer 12 and the refractiveindex anisotropic layer 13 is excellent, and the durability of eachlayer is excellent. Therefore, the problem of peeling off of therefractive index anisotropic layer 13 can be solved effectively.

Moreover, in this embodiment, by making the average curing degree of therefractive index anisotropic layer 13 of the finally manufacturedoptical element 10 is 90% or more, the adhesion with respect to thealignment property providing layer 12 can further be improved. Moreover,even in the case the optical element 10 is rolled up, the problem ofblocking, generated by the refractive index anisotropic layer 13sticking onto the rear surface of the transparent base material 11, isnot generated. Therefore, the problem of peeling off of the refractiveindex anisotropic layer 13, the rising of the haze and unevennessgeneration or the like, generation deriving from the alignment failure,can be solved more effectively.

EXAMPLES

Next, specific examples of the above-mentioned embodiments will bedescribed.

Example 1

First, by adding a cyclohexanone (98 parts by weight) to an alignmentfilm composition, including a polymer having a cinnamoyl group (2.0parts by weight), and dissolving, a solution of an alignment filmcomposition was obtained. Then, after coating this solution onto atriacetyl cellulose (TAC) film (thickness 80 μm), as the transparentbase material, by a wire bar coater, it was dried for 2 minutes with hotair of 80° C. Thus, a 0.1 μm thickness coated film was obtained. Byirradiating a polarized ultraviolet ray to the coated film by 10 mJ/cm2,an alignment film with the alignment limiting force exhibited on thesurface was formed.

Next, a solution of a liquid crystalline composition was obtained by:dissolving a liquid crystalline composition, including a polymerizablenematic liquid crystal compound represented by the above-mentionedchemical formula (I), into a toluene solution by a 20% by mass ratio;and furthermore, adding a polymerization initiator (IRGACURE 907(product name), manufactured by Chiba Speciality Chemicals). Then, bycoating this solution onto the alignment film, produced in theabove-mentioned process, by a wire bar coater and drying, a 1 μmthickness coated film was obtained. Next, by heating the coated film at85° C. for 2 minutes, the liquid crystal molecules in the coated filmwere aligned by the alignment limiting force exhibited on the surface ofthe alignment film. Thereafter, a 300 mJ ultraviolet ray was irradiated,under the air atmosphere, utilizing a high pressure mercury lamp forcuring the coated film. Thus, the alignment state of the liquid crystalmolecules was fixed. Thereby, a nematic liquid crystal layer was formedon the alignment film, so as to finally manufacture an optical elementin this example.

Example 2

First, according to the same method as in the above-mentioned example 1,an alignment film was formed on a triacetyl cellulose (TAC) film as thetransparent base material.

Next, a solution of a liquid crystalline composition was obtained by:dissolving a liquid crystalline composition, including a polymerizablenematic liquid crystal compound represented by the above-mentionedchemical formula (I), into a toluene solution by a 20% by mass ratio;and furthermore, adding a polymerization initiator (IRGACURE 907(product name), manufactured by Chiba Speciality Chemicals). Then, bycoating this solution onto the alignment film, produced in theabove-mentioned process, by a wire bar coater and drying, a 1 μmthickness coated film was obtained. Next, by heating the coated film at85° C. for 2 minutes, the liquid crystal molecules in the coated filmwere aligned by the alignment limiting force exhibited on the surface ofthe alignment film. Thereafter, a 100 mJ ultraviolet ray was irradiated,under the nitrogen atmosphere, utilizing a high pressure mercury lampfor curing the coated film. Thus, the alignment state of the liquidcrystal molecules was fixed. Thereby, a nematic liquid crystal layer wasformed on the alignment film, so as to finally manufacture an opticalelement in this example 2.

Comparative Example

First, according to the same method as in the above-mentioned example 1,an alignment film was formed on a triacetyl cellulose (TAC) film as thetransparent base material.

Next, a solution of a liquid crystalline composition was obtained by:dissolving a liquid crystalline composition, including a polymerizablenematic liquid crystal compound represented by the above-mentionedchemical formula (I), into a toluene solution by a 20% by mass ratio;and furthermore, adding a polymerization initiator (IRGACURE 907(product name), manufactured by Chiba Speciality Chemicals). Then, bycoating this solution onto the alignment film, produced in theabove-mentioned process, by a wire bar coater and drying, a 1 μmthickness coated film was obtained. Next, by heating the coated film at85° C. for 2 minutes, the liquid crystal molecules in the coated filmwere aligned by the alignment limiting force exhibited on the surface ofthe alignment film. Thereafter, a 100 mJ ultraviolet ray was irradiated,under the air atmosphere, utilizing a high pressure mercury lamp forcuring the coated film. Thus, the alignment state of the liquid crystalmolecules was fixed. Thereby, a nematic liquid crystal layer was formedon the alignment film, so as to finally manufacture an optical elementin this comparative example.

(Evaluation Result)

The curing degree of the nematic liquid crystal layer of each opticalelement of the example 1, the example 2 and the comparative example wasmeasured. The curing degree was obtained by cutting the nematic liquidcrystal layer with the oblique cutting method and subsequently measuringthe obtained cross-sectional surface of the layer by the followingprocess: the intensity distribution of the stretching vibration of thedouble bond (C═C) of the carbons attributing to the reactive groups ismeasured by using the reflection measuring method of a microscopeinfrared spectrophotometer. The results are shown in the table 1 below.

As shown in the table 1, the average curing degree of the opticalelement obtained in the example 1 was 98% and a curing gradient wasgenerated. The optical element obtained in the example 2 generated acuring gradient, but the optical element showed a lower curing degree of85%, when compared to the example 1.

On the other hand, the optical element of the comparative example 1showed a curing degree of 85%, but generated no curing gradient.

Moreover, the results of visibly evaluating the alignment property ofthe liquid crystal molecules for each optical element of the example 1,the example 2 and the comparative example are shown in the followingtable 1. As it is apparent from the following table 1, the alignmentstate of the liquid crystal molecules was homogeneous in the opticalelements of the example 1 and the comparative example. Moreover, whenthe optical element of the comparative example was rolled up and left,the nematic liquid crystal layer was stuck onto the rear surface of theTAC film so as to generate blocking, and furthermore, the alignmentstate of the liquid crystal molecules was also disturbed.

Furthermore, for each optical element of the example 1, example 2 andthe comparative example, as a test for evaluating the adhesion, alattice pattern tape peeling test was carried out based on the JIS 5400.Specifically, using a Sellotape (registered mark) (CT24, manufactured byNICHIBAN CO., LTD.), after sticking the same to the film, with the ballof a finger, it was peeled off. The judgment was made based on thenumber of the squares, those were not peeled off, out of 100 squares.The case with the nematic liquid crystal layer was not peeled off at allis 100/100, and the case completely peeled off is 0/100. The results areshown in the following table 1. As it is apparent from the followingtable 1, the optical element of the comparative example did not have apreferable adhesion.

TABLE 1 Refractive index anisotropic layer curing degree (%) LiquidAlignment crystal property Average alignment Air providing curingproperty Adhesion side layer side degree Example 1 Homogeneous ◯ 95 9998 alignment (100/100) Example 2 Inhomogeneous Δ 84 86 85 alignment (40/100) Comparative Homogeneous X 98 98 98 example alignment  (0/100)

1. A method for manufacturing an optical element comprising: a step ofpreparing a transparent base material with an alignment film, made froma alignment film composition capable of exhibiting an alignment limitingforce by a photo-alignment method, laminated thereon as an alignmentproperty providing layer; a step of coating a liquid crystallinecomposition including a polymerizable liquid crystal material onto thealignment property providing layer of the transparent base material; anda step of forming a refractive index anisotropic layer, comprising aliquid crystal layer, whose curing degree changes monotonously with apredetermined gradient in its thickness direction, on the alignmentproperty providing layer of the transparent base material by curing theliquid crystalline composition while delaying a curing rate of theliquid crystalline composition near a surface on the side not adjacentto the alignment property providing layer, compared with the curing ratenear a surface on the side adjacent to the alignment property providinglayer.
 2. The method for manufacturing an optical element according toclaim 1, wherein, in the step of forming the refractive indexanisotropic layer, a radioactive ray is irradiated to the liquidcrystalline composition in a state that, among the liquid crystallinecomposition, only the side not adjacent to the alignment propertyproviding layer is exposed to an air atmosphere.
 3. The method formanufacturing an optical element according to claim 2, wherein theradioactive ray is an ultraviolet ray, and the liquid crystallinecomposition includes a polymerization initiator together with thepolymerizable liquid crystal material.